Implantable medical devices (IMDs) are devices designed to be implanted into a patient. Some examples of these devices include cardiac function management (CFM) devices such as implantable pacemakers, implantable cardioverter defibrillators (ICDs), cardiac resynchronization devices, and devices that include a combination of such capabilities. CFM devices are typically used to treat patients using electrical or other therapy. They can also help a physician or caregiver in diagnosing a patient by internal monitoring of the patient's condition. CFM devices may include one or more electrodes in communication with one or more sense amplifiers to monitor electrical heart activity within a patient. CFM devices often include one or more other physiological sensors to monitor one or more other internal patient parameters. Other examples of implantable medical devices include implantable diagnostic devices, implantable drug delivery systems, or implantable devices with neural stimulation capability.
Additionally, some IMDs detect events by monitoring intrinsic electrical heart activity signals. CFM devices may also measure one or more hemodynamic parameters, for example, related to heart chamber filling and contractions. Ischemia occurs when blood flow to cardiac muscles decreases below the metabolic needs of the heart. Ischemia impairs the pumping function of the heart. Increased heart rate may be a risk factor for patients who have experienced ischemia. Drug therapy may reduce heart rate but the use of drugs may be limited by negative effects or contraindications.